A sliding coupling has the great advantage of simplicity in use over threaded couplings. There are various types of sliding couplings, the one shown in Rassieur U.S. Pat. No. Re. 26,938 being one. Others have three or more keys instead of two, and may not provide an O-ring seal. Still others use a noncircular coupling, e.g., octagonal, which eliminates the need for keys.
In all of these couplings, there is the problem of fine sand's getting into the joint so that the joints will not easily slide apart. It is frequently necessary to beat on the joint to loosen the sand. In the Rassieur joint shown in Re. 26,938, the O-ring seal prevents sand from getting into the joint from outside the auger, but in drilling in sand below the water table, sand can get into the joint from inside the hollow stem auger.
It has been found that by providing a slight taper of the sliding coupling surfaces, the problem of binding of the joints with fine sand can be eliminated.
One of the objects of this invention is to provide a simple drill string joint that can be uncoupled in spite of the presence of fine sand between the coupling surfaces.
Other objects will become apparent to those skilled in the art in the light of the following description and accompanying drawing.